Hemirhamphodon sesamum, Tan & Lim, 2013
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publication ID |
https://doi.org/ 10.5281/zenodo.5352848 |
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persistent identifier |
https://treatment.plazi.org/id/038487FB-AB70-FF8A-FF04-FF43FAECFDE7 |
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treatment provided by |
Tatiana |
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scientific name |
Hemirhamphodon sesamum |
| status |
sp. nov. |
Hemirhamphodon sesamum View in CoL , new species
( Figs. 1A–D View Fig , 2A–C View Fig , 3A, B View Fig , 4 View Fig , 5A–D View Fig , 6A–B View Fig )
Material examined. — Holotype – MZB 17209, 36.7 mm SL, male; Indonesia: South Kalimantan: Batulicin basin; stream at Simpang Alok, along road from Batulicin to Mantewe , Desa Gunung Raya (84 m asl); H. Tommy et al., 14 Sep.2011.
Paratypes – MZB 17210, 7 ex., 19.2–44.4 mm SL; same locality as holotype . – ZRC 54009, 37 ex., 18.2–46.4 mm SL; Indonesia: South Kalimantan: Cantung basin; north of Batulicin, Sei Kupang area , amidst limestone hills (24 m asl, pH 8.0); H. Tommy et al., 12 Sep.2011 . – ZRC 54010, 10 ex., 13.4–44.6 mm SL; Indonesia: South Kalimantan: Batulicin basin; hill stream at foothills of Gunung Kukusan on northeast side (52 m asl); H. Tommy et al., 12 Sep.2011 . – ZRC 54013, 2 ex., 41.4–47.4 mm SL; Indonesia: South Kalimantan: north of Batulicin ; T. Idei, 2004. CMK 16796, 4 ex., 34.5–46.4 mm SL; Indonesia: South Kalimantan: 25 km south of Damar Datar , Koto to Batulian ; T. Idei , 12 Oct.2000 .
Diagnosis. — Hemirhamphodon sesamum differs from all congeners in having the following suite of characters: 1) Dorsal fin with melanophores in two distinct sizes – for males in life ( Figs. 2A View Fig , 4 View Fig ), first 6 to 7 rays distal one-third to half with yellow suffused throughout the rays and interradial membrane, with iridescent red margin; intense black pigments on the mid-section of interradial membrane between first 3 rays; red pigments on the mid-section of interradial membrane between 6 to 11 rays; rest of fin hyaline. For males in preservative ( Fig. 2B, C View Fig ), colour pattern as above, but the iridescent red margin is absent. For females in life ( Fig. 3A View Fig ), first 6 to 7 rays suffused with pale yellow, with iridescent red margin; small patches of black pigments on the middle section of the interradial membrane of first 6 to 7 rays; rest of fin hyaline. For females in preservative ( Fig. 3B View Fig ), colour pattern as above, but the iridescent red margin is absent. Black patches on anterior portion of dorsal fin present in specimens 20 mm SL or larger. 2) Unique dorsal fin morphology in the males ( Fig. 4 View Fig ) – distal portions of first 6 to 7 rays elongated, free of interradial membrane, projected into filaments up to twice the depth of the dorsal fin; adpressed fin rays reaching caudal-fin base and beyond. 3) Unique colouration on lower jaw; for males in life ( Fig. 5A View Fig ), upper jaw with corresponding portion of lower jaw yellow; dorsal surface of exposed lower jaw bluish, dermal flange below middle section of lower jaw bright red with blue lower margin, tip of lower jaw to region below upper jaw red; dermal flange of lower jaw with distinct black ventral margin from tip to region directly below eye. Males in preservative ( Fig. 5B View Fig ) exhibit similar colour pattern but colours are subdued or faded. Females in life ( Fig. 5C View Fig ) have similar colour pattern as male but colours are comparatively less intense. For females in preservative ( Fig. 5D View Fig ), the red band on the dermal flange of the lower jaw is replaced by yellow. 4) Males with the fourth anal-fin ray distinctly enlarged ( Figs. 1A, B View Fig , 2A–C View Fig , 6A View Fig ), and third, fourth and eighth anal-fin rays branched; females with third and fourth anal-fin rays branched ( Figs. 1C, D View Fig , 3A, B View Fig , 6B View Fig ). 5) Pelvic-fin origin anterior to dorsal-fin origin. 6) Dorsal-fin rays 13 or 14 (mode 13).
Description. — See Figs. 1–5 View Fig View Fig View Fig View Fig View Fig for general appearance and Table 1 for morphometric data.
Head short (head length 24.3–28.7% SL) and body slender and long (body depth 8.6–11.9% SL, caudal peduncle depth 4.7–5.7% SL, body length 70.5–75.3% SL). Lower jaw about half of body length (48.0–63.8% BL), about 1.2–1.7 times head length; usually straight, tip bent downwards in a few specimens; dermal flange of lower jaw on male deeper than that on female. Dorsal-fin origin anterior to anal-fin origin, posterior to pelvic-fin origin, situated nearer to caudal fin (predorsal length 71.7–76.9% SL), dorsal-fin base short (dorsal-fin base length 18.9–24.5% SL); dorsal-fin rays 13 or 14 (mode 13); male with first 6 to 7 dorsal-fin rays elongated into filaments, adpressed rays reaching caudal-fin base and beyond. Caudal fin elongate, rounded, caudal-fin rays 26. Anal-fin rays 8 (last ray split to base), with short base (5.8–9.2% SL), male with distinct posterior projection on base of fourth fin ray, adpressed elongated anal-fin ray reaching caudal-fin base, with branched ray on rays 3, 4 and 8, andropodium developed on ray 5 to 8, rays 5 and 8 thickened throughout ( Fig. 5A View Fig ); female with branched ray on rays 3 and 4 ( Fig. 5B View Fig ). Pelvic-fin rays 6–7, fins are adpressed to body, male with longer inner rays, adpressed rays reaching anal-fin origin; female with shorter rays, adpressed rays not reaching anus. Pectoral-fin rays 8, rounded. Precaudal vertebrae 23–26, caudal vertebrae 14–16; total vertebrae 38–41 (mode 40, n = 20). First gill arch with up to 13 gill rakers. Maximum size 47.4 mm SL.
Colouration in life. — See Figs. 1A, 1C View Fig , 2A View Fig , 3A View Fig , 5A, 5C View Fig . Adult male – Head brown on dorsum and sides, ventrum cream. Upper jaw yellow with corresponding portion of lower jaw also yellow; dorsal surface of exposed lower jaw bluish, middle section of dermal flange on lower jaw red with blue lower margin, red section from tip to region below upper jaw; ventrum of lower jaw flange with distinct black margin from tip to region directly below eye. Eye with upper half of iris pale reddish. Operculum with scattering of melanophores, and pinkish on posterior part. Body with brown dorsal stripe, dorsum pinkish and sides yellowish brown, ventrum cream with thin reddish ventral stripe. Dorsal fin with first 6 to 7 rays distal one-third to half with yellow suffused throughout the rays and interradial membrane; intense black pigments on the mid-section of interradial membrane between first 3 rays; red pigments on the mid-section of interradial membrane between 6 to 11 rays; rest of fin hyaline. Caudal, anal and pelvic fins with bright red margin; anal fin with bright red blotch on middle of andropodium. Pectoral fins hyaline.
Adult female: colouration similar, but less intense. Dorsal fin with first 6 to 7 rays suffused with pale yellow, with iridescent red margin; small patches of black pigments on the middle section of the interradial membrane of first 6 to 7 rays; rest of fin hyaline.
Colouration in preservative. — See Figs. 1B, D View Fig , 2B, C View Fig , 3B View Fig , 5B, D View Fig .
Adult male – Head brown on dorsum and sides, ventrum cream. Upper jaw yellow with corresponding portion of lower jaw also yellow; dorsal surface of exposed lower jaw bluish, middle section of dermal flange on lower jaw red with blue lower margin, red section from tip to region below upper jaw; ventrum of lower jaw flange with distinct black margin from tip to region directly below eye. Eye with upper half of iris pale reddish. Operculum with scattered melanophores, pinkish on posterior part. Body with brown dorsal stripe, dorsum pinkish and sides yellowish brown, ventrum cream with thin reddish ventral stripe (may be faint on specimens preserved for a long time). Dorsal fin with first 6 to 7 rays and distal one-third to half suffused with yellow throughout the rays and interradial membrane; intense black pigments on the mid-section of interradial membrane between first 3 rays; red pigments on the mid-section of interradial membrane between 6 to 11 rays; rest of fin hyaline. Caudal, anal, pelvic and pectoral fins hyaline.
Adult female – colouration as for male, but subdued. All fins hyaline. Black patches on anterior portion of dorsal fin in specimens larger than or equal to 20 mm SL.
Distribution. — Hemirhamphodon sesamum is currently known only from South Kalimantan, Indonesian Borneo, in lowland drainages of the Batulicin and Cantung basins that drain eastwards into the Makassar Strait ( Fig. 7 View Fig ).
Field notes. — Hemirhamphodon sesamum inhabits clear flowing waters of small streams, about 2–5 m wide and up to 2 m deep, with sand and gravel bottoms (see Fig. 8 View Fig ). It tends to form small groups of 3 to 5 individuals at the surface, preferring quiet pools near or under overhanging bank vegetation. Syntopic ichthyofauna includes: Hampala macrolepidota , Osteochilus cf. waandersii , Rasbora dies , R. elegans , R. lacrimula , Systomus anchisporus , S. banksi (Cyprinidae) , Balitoropsis stephensoni , Homalopteroides nebulosus (Balitoridae) , Nemacheilus cf. spiniferus (Nemacheilidae) , Betta edithae (Osphronemidae) , Channa lucius (Channidae) , and Macrognathus maculatus (Mastacembelidae) .
Etymology. — The species name refers to the minute oily seeds of the Sesamum plant ( Pedaliaceae ); in allusion to the small black spots/dashes on the dorsal fin with which resemble black sesame seeds. Used as a noun in apposition.
Comparisons with congeners. — Hemirhamphodon sesamum shares with H. pogonognathus , H. kuekenthali , H. byssus , and H. kecil a posterior projection on the fourth anal-fin ray, a similar range of dorsal-fin rays (12–17) and a similar number of vertebrae (37–44). Hemirhamphodon sesame further shares with H. kuekenthali and H. byssus two types of melanophore on the dorsal fin.
Hemirhamphodon sesamum seems to be most closely related to H. kuekenthali in terms of external morphology. The current distribution of H. kuekenthali within Borneo ( Kottelat & Lim, 1995; pers. obs.) is from central to northern Sarawak and Brunei Darussalam. While H. sesamum is currently known only from the southernmost tip of Borneo. It seems to represent a vicariant distribution. The ichthyofauna of the short coastal basins in South Kalimantan draining into the Makassar Straits is poorly known.As evident from other parts of Southeast Asia where short coastal basins are present, such as the western coast of Sumatra ( Lumbantobing, 2010), the rate of endemism is expected to be relatively high.
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